Palpitation is the PERCEPTION of heart beats. Humans are not aware of their heart beats, of their breath, their digestion etc, but sometimes humans can feel them, localize them (diffuse or specific) and describe them as pain, pyrosis, constriction etc. Those symptoms may associate, as Arrihan said, sweating, dizziness or anxiety but this is not mandatory.
So humans can sometimes be aware of their normal or abnormal heartbeats and other activities happening in their respiratory or digestive system.
It is physiological for all of us to have 3-4 extra beats per day either we feel them or not. Of course, there are triggers like increased coffee consumption, hypertension, high thyroid hormones level etc so we must choose a healthy routine avoiding those risk factors like smoking, sleep deprivation, long term stress and also consult the doctor from time to time for prevention.
Take care! :)
RE: What causes palpitations